1. Field of the Invention
The present invention generally relates to amplifiers for solid state photodetectors and imagers, and more particularly to a technique for achieving integer gain for analog charge packets. The technique employs multiple non-destructive readout (NDRO) and summation of analog charge packets to provide an amplifier-per-detector in single detectors and in one and two dimensional arrays of detectors.
2. Description of the Prior Art
Conventional low noise amplifiers are used with optical and infrared detectors for image sensing in many applications. Multiple metal oxide semiconductor field effect transistor (MOSFET) amplifiers have been incorporated into very large charge injection device (CID) sensors, as illustrated for example in G. J. Michon U.S. Pat. No. 4,807,038, issued Feb. 21, 1989 and assigned to the instant assignee. The Michon patent is hereby incorporated by reference. Extremely low loss non-destructive readout (NDRO) of CID image sensors has been demonstrated, with a loss of less than one electron per readout, during continuous NDRO of a stored image. See, for example, "CID Image Sensing" by G. J. Michon and H. K. Burke, Chapter 2, "Charge Coupled Devices", D. F. Barbe (ed), Topics in Applied Physics, Vol. 38, Springer-Verlag, Berlin, Heidelberg, N.Y. (1980).
This technique has been used with CID sensors at Kitt Peak National Observatory to produce very wide dynamic range astronomical images as reported by R. S. Akins, C. R. Lynds and R. E. Nelson in "Astronomical Applications of Charge Injection Devices", Low Light Level Devices, Society of Photo-Optical Instrumentation Engineers, Vol. 78 (1976) , pp. 65-71. In addition, E. R. Fossum and R. C. Barker, in "A Linear and Compact Charge-Coupled Charge Differencer/Replicator", IEEE Transactions on Electron Devices, Vol. ED-31, No. 12, Dec. 1984, pp. 1784-1789, describe a charge-coupled circuit for creating a charge packet equal to the difference of two input charge packets.
Optical, infrared, X-ray, and a host of other detectors are performance limited by noise introduced subsequent to the detection process. Amplification at the detection site, prior to the introduction of Johnson noise from conductors, conventional amplifiers and switching noise, would offer significant performance improvements. Arrays of detectors with multiple channels also suffer from variations in offset and gain between the various channels. A charge amplification technique with precise, integer gain that could be used at each of an array of detectors would also offer significant performance improvements against offset and gain variations.